The upshot of this is that LLMs are quite good at the stuff that he thinks only humans will be able to do. What they aren't so good at (yet) is really rigorous reasoning, exactly the opposite of what 20th century people assumed.
Alfred Bester's "The stars my destination" stands out as a shining counterpoint in this era. You don't get much character development like that in other works until the sixties imo.
Yeah, I'd say characterisation is a weakness of his. I've read Stranger in a Strange Land, The Moon is a Harsh Mistress, Starship Troopers, and Double Star. Heinlein does explore characters more than, say, Clark, but he doesn't go much for internal change or emotional growth. His male characters typically fall into one of two cartoonish camps: either supremely confident, talented, intelligent and independent (e.g. Jubal, Bernardo, Mannie, Bonforte...) or vaguely pathetic and stupid (e.g. moon men). His female characters are submissive, clumsily sexualised objects who contribute very little to the plot. There are a few partial exceptions - e.g. Lorenzo in Double Star and female pilots in Starship Troopers - but the general atmosphere is one of teenage boy wish fulfilment.
In entire fairness, I was distracted by you having said he and his contemporaries must all have been autistic, as if either you yourself were remotely competent to embark upon any such determination, or as though it would in some way indict their work if they were.
I'm sure you would never in a million years dare utter "the R-slur" in public, though I would guess that in private the violation of taboo is thrilling. That's fine as far as it goes, but you really should not expect to get away with pretending you can just say "autistic" to mean the same thing and have no one notice, you blatantly obvious bigot.